JPH08257404A - Oxide catalyst material for removing nitrogen oxide and method for removing nitrogen oxide - Google Patents

Abstract

(57) [Summary] [Purpose] W / F in the presence of water vapor or high oxygen concentration atmosphere
Even if the value is high, it has a high NO _x reduction decomposition effect in a wide range even in low temperature range, and purifies exhaust gas of various internal combustion engines for energy saving, resource saving and prevention of global warming and harmful substances containing NO _x . [Structure] Ni as an oxide catalyst material for removing nitrogen oxides
A Pt or Pd is supported on a carrier whose main crystal phase containing Al and Ga as main metal elements is a spinel-type composite oxide and alumina to form an oxide catalyst material for removing nitrogen oxides. The material is brought into contact with an exhaust gas containing nitrogen oxides in an oxidizing atmosphere in which a high concentration of oxygen is present and a reducing gas such as a hydrocarbon is present to reduce and decompose the nitrogen oxides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel oxide catalyst material capable of reducing and removing nitrogen oxides, and a method for removing nitrogen oxides in exhaust gas using the same, and more particularly to exhaust gas. The present invention relates to a catalyst for nitrogen oxide reduction and removal in diesel engines and the like having a low temperature, and a method for removing nitrogen oxide in exhaust gas at low temperature using the catalyst.

[0002]

2. Description of the Related Art In recent years, air pollution caused by various pollutants has become a major social problem, and among them, harmful substances such as NO _x and CO _{x in} exhaust gas of automobiles, which are sources of migration of air pollution, are decomposed. There is an urgent need to develop a method for removal.

Conventionally, NO _x , C in the exhaust gas of automobiles
Decomposing harmful substances O _X such as a method of removing, using an oxidation of carbon monoxide (CO) and hydrocarbons (C _X H _X), nitrogen oxide three-way catalyst to perform reduction at the same time the (NO _X) The method has been adopted.

As a three-way catalyst used in such a method, a refractory material such as cordierite coated with γ-alumina (Al ₂ O ₃ ) is used, and palladium (Pd) or platinum (Pd) is used.
t) and those carrying a noble metal such as rhodium (Rh) have been used.

However, although the three-way catalyst can efficiently purify the exhaust gas only at a low oxygen concentration of about 0.5%, the three-way catalyst has a high oxygen concentration of more than 1%. It has the drawback of not working effectively in the region.

Therefore, normally, the oxygen concentration in the exhaust gas is measured, and the air-fuel ratio is controlled so that CO, C _X H _X , and NO _X can be processed at a high purification rate, and the air-fuel ratio is in a range close to the theoretical equivalent value. However, the CO and C _X H _X , and N
Since O _X generation mechanisms have contradictory properties, it is necessary to support combustion in a state where limited exhaust gas purification at a high oxygen concentration in than it is at present, not hardly.

Further, since energy saving and resource saving have recently been demanded, in a gasoline engine, research and development of a lean combustion system have been carried out in order to achieve low fuel consumption. Has a disadvantage that the noble metal of the catalyst cannot be purified by exhaust gas due to oxygen poisoning.

Also in the diesel engine, in the present combustion system, the exhaust gas is not purified at all because the oxygen concentration in the exhaust gas is high.

On the other hand, it occurs at a high temperature of about 1000 ° C. or higher,
As a method of effectively purifying NO _X , the concentration of which increases as the combustion temperature increases, there is a selective catalytic reduction method using ammonia in addition to the above method. Although effective for purifying NO _{x in} high exhaust gas, applying this method to a mobile combustion device such as an automobile has a problem in safety.

[0010] Therefore, as to solve the above problems, a method of the hydrophobic zeolite carrying the metal removing NO _X while in contact with the hydrocarbon as a catalyst, is proposed in JP-A 4-349938 Patent Publication There is.

[0011]

However, a catalyst using the above-mentioned metal-supporting hydrophobic zeolite as a catalyst has poor water resistance. For example, when water is contained in exhaust gas such as a diesel engine, water vapor NO _X by existence
There is a problem that the purification rate of
Even in heat resistance, the catalyst has problems such as structural destruction,
A catalyst material having excellent heat resistance and water resistance and having NO reduction activity over a wide range up to a low temperature region of 350 ° C. or less has been desired.

[0012]

SUMMARY OF THE INVENTION The present invention does not require a highly toxic reducing agent such as ammonia, and allows a relatively low temperature exhaust gas having a high oxygen concentration containing water such as a diesel engine to have a high flow velocity. Even so, it is intended to provide a catalyst material which is capable of effectively purifying NO _X in exhaust gas and which has excellent heat resistance and has a wide NO reduction activation temperature range, and a nitrogen oxide removing method using the same.

[0013]

The present invention has been made in view of the above problems, and provides a composite oxide having a spinel structure as a crystal phase containing nickel (Ni) and gallium (Ga) as main metal elements. Alumina (Al ₂ O ₃ )
An oxide catalyst material in which platinum (Pt), which is a noble metal, is supported on a carrier in which is mixed, has an excellent low-temperature activity with a maximum catalytic activity in a low temperature range of 300 ° C or lower even in a high oxygen concentration in the presence of water vapor. In addition, palladium (P
It has been discovered that the oxide catalyst material supporting d) has excellent catalytic activity over a wide temperature range of 300 ° C. to 500 ° C. for a long time even at a high oxygen concentration in the presence of water vapor.

That is, the oxide catalyst material for removing nitrogen oxides of the present invention contains a composite oxide powder containing nickel (Ni) and gallium (Ga) as main metal elements and having a crystal phase having a spinel type structure. 0.01 to 1.0 part by weight of platinum (Pt) or palladium (Pd) is carried on a carrier mixed with Al ₂ O ₃ powder based on 100 parts by weight of the carrier. .

In particular, the platinum (Pt) is added to the carrier 10.
0.03 to 1.0 part by weight with respect to 0 part by weight, or 0.01 to 0.7 part by weight of the palladium (Pd) with respect to 100 parts by weight of the support, and an oxide catalyst material. Is more preferable, and in particular, the platinum (Pt) is less than 0.
It is most preferable to carry 03 to 0.7 parts by weight, or 0.01 to 0.5 parts by weight of the palladium (Pd).

Further, the method for removing nitrogen oxides of the present invention contains nickel (Ni) and gallium (Ga) as main metal elements in an oxidizing atmosphere in which a high concentration of oxygen and a carbon-containing gas having a reducing property are present. To a carrier prepared by mixing Al ₂ O ₃ with a complex oxide whose crystal phase is a spinel structure,
The carrier 1 containing platinum (Pt) or palladium (Pd)
It is characterized in that the exhaust gas containing nitrogen oxides is brought into contact with the oxide catalyst material which is supported by 0.01 to 1.0 parts by weight with respect to 00 parts by weight.

Above all, the platinum (Pt) as the oxide catalyst material is 0.1% based on 100 parts by weight of the carrier.
It is more desirable to use 03 to 1.0 parts by weight, or 0.01 to 0.7 parts by weight of the palladium (Pd) supported on 100 parts by weight of the support, and further the platinum (Pt). It is most preferable to use 0.03 to 0.7 part by weight of Pd, or 0.01 to 0.5 part by weight of the palladium (Pd).

In the present invention, as the oxide catalyst material for removing nitrogen oxides, platinum (Pt) or palladium (Pd), which is a noble metal, is added to the support in an amount of less than 0.01 part by weight based on 100 parts by weight of the support. In the case of only supporting it, NO reduction activity does not appear in the low temperature region of 350 ° C. or lower, and conversely, when it exceeds 1.0 part by weight, only the simple oxidation reaction of the reducing agent proceeds, and the NO reduction reaction occurs. It does not appear.

Therefore, in the oxide catalyst material for removing nitrogen oxides, platinum (Pt) or palladium (Pd) is added to the support in an amount of 0.01 to 100 parts by weight.
The amount of platinum (Pt) is limited to 1.0 part by weight, and from the viewpoint of catalytic activity, platinum (Pt) is 0.03 to 1.0 part by weight, or palladium (P) is added to 100 parts by weight of the support.
0.01 to 0.d) based on 100 parts by weight of the carrier.
It is more desirable to support 7 parts by weight, and especially from the viewpoint of catalytic activity in a wide temperature range, the platinum (Pt)
0.03 to 0.7 parts by weight with respect to 100 parts by weight of the carrier, or the palladium (Pd) added to the carrier 10.
It is most preferable to support 0.01 to 0.5 parts by weight with respect to 0 parts by weight.

The composite oxide contains nickel (Ni) and gallium (Ga) as main metal elements and has a spinel type crystal phase represented by NiGa ₂ O ₄ as a general formula. The correlation between Ni and Ga of the composite oxide is preferably 1.4 or more, and most preferably 1.5 or more, from the viewpoint of catalytic activity, in terms of the count ratio of Ga to Ni by fluorescent X-ray analysis.

Further, it is considered appropriate that the Al ₂ O ₃ has a high specific surface area, and 60 m ² is practically used.
/ G or more is desirable, and although the change in catalyst activity due to the Al ₂ O ₃ mixed amount is small, the mixed amount is 20 to 70.
Weight percent is preferred and 25-60 weight percent is most desirable.

Further, platinum (Pt) or palladium (Pd), which is a noble metal, is added to a carrier obtained by mixing the composite oxide with Al ₂ O ₃ in a total amount of 0.01 to 1. When the oxide catalyst material supporting 0 parts by weight and the exhaust gas containing nitrogen oxides are brought into contact with each other, C ₂ H ₄ , C ₃ H ₆ , and C ₃ H ₈ as reducing agents are introduced into the exhaust gas atmosphere.
Hydrocarbons etc., CH ₃ OH, and alcohols such as C ₂ H ₅ OH, contain a carbon gas or the like having a reducing CO or the like, when contacted with the catalyst material, NO _X reducing is further increased .

[0023]

According to the oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention, the oxide catalyst material is N
Platinum (Pt) or palladium (Pd) was added to a carrier in which a complex oxide containing i and Ga as main metal elements and having a crystal phase having a spinel structure and Al ₂ O ₃ was mixed.
Since 0.01 to 1.0 part by weight was carried with respect to 100 parts by weight of the carrier, the hydrocarbon activated by the NO ₂ carried by the NO ₂ produced by the oxidation reaction of NO on the carrier and the noble metal carried by the carrier. Reacts and exhibits NO reduction activity even in a low temperature range of 350 ° C. or lower.

[0024]

EXAMPLES Hereinafter, the oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention will be described in detail based on examples.

The oxide catalyst material for removing nitrogen oxides of the present invention is obtained by weighing a predetermined amount of raw material powder containing Ni and Ga,
After sufficiently stirring and mixing, Al ₂ O ₃ powder was added, and heat treatment was performed at a temperature of 500 to 1600 ° C. for 5 to 30 hours in an oxidizing atmosphere to form a composite of spinel-type crystals containing Ni and Ga as main metal elements. A mixed powder of oxide and Al ₂ O ₃ is obtained.

Next, using the mixed powder as a carrier, an aqueous solution containing a predetermined amount of a noble metal is added, and the mixture is evaporated to dryness, and then heated in a helium (He) gas at a temperature of 400 to 600 ° C. for 3 to 3.
After heat treatment for 5 hours, the oxide catalyst material of the present invention is obtained.

As the raw material powder, for example, oxides of Ni and Ga, and their carbonates, nitrates, acetates and the like which generate oxides by heat treatment can be used.

Further, it is considered that the raw material powder improves the reductive decomposition property of NO _x by solid-dissolving Ga metal in NiGa ₂ O ₄ having a stoichiometric spinel structure. It is desirable to mix them so that the element ratio is 2.1 or more.

Further, the above-mentioned composite oxide can be synthesized by a solid-phase reaction with oxides or other metal salts other than the above, or by a sol-gel method of metal alkoxide, etc., and is not limited to these production methods. It is not something that will be done.

The temperature of the heat treatment of the mixed powder is 50
If the temperature is lower than 0 ℃, the crystallization will be insufficient, and conversely 1600 ℃.
If it exceeds, it will be densified, so it is 500-1600 ℃
At a temperature of 5 to 30 hours in an oxidizing atmosphere, but heat treatment at a particularly low temperature is effective for increasing the specific surface area of the powder, and practically the specific surface area is 60 m ² / g or more. It is desirable to set

Next, in evaluating the present invention, Ni (NO ₃ ) ₂ .6H ₂ O and Ga (NO ₃ ) _{3 were used} as starting materials.
-Using a reagent of 9H ₂ O, weighed so that the metal element ratio of Ni and Ga was 1: 3, dissolved these reagents in distilled water, and neutralized with ammonia water while stirring.
50 parts by weight of Al ₂ O ₃ powder was added to 100 parts by weight of the resulting precipitate, and the mixture was sufficiently stirred and mixed by an ultrasonic emulsification disperser, and then freeze-dried.

Next, the dry powder was heat-treated in the air at a temperature of 700 ° C. for 30 hours, then an aqueous solution containing each noble metal in an amount shown in Table 1 was added to the powder, and the mixture was evaporated to dryness. In a helium (He) stream, heat treatment was performed at a temperature of 500 ° C. for 3 hours.

Thereafter, the powder carrying the noble metal is molded by a die press, CIP-molded, the molded body is crushed and sieved, and the size of the powder exceeds 500 μm and 700 μm or less to obtain a sample for evaluation. Prepared.

A comparative example was one in which no noble metal was supported on the carrier.

The count ratio of Ga to Ni obtained by fluorescent X-ray analysis of the evaluation sample thus obtained was 1.
It was 93.

Further, the crystal phase was identified by X-ray diffraction measurement (XRD), and it was confirmed that the crystal phase consisted of a spinel crystal and a γ-Al ₂ O ₃ phase.

Next, NO of 1000 ppm and O ₂ of 1
0%, H ₂ O 10%, C ₂ H ₄ 100 as reducing agent
A reaction gas containing water vapor of 0 ppm and the rest being He is used as a condition for contacting the reaction gas with the catalyst material.
/ F was set to 0.03 g · sec / cc, the sample for evaluation was flowed through the catalyst layer, and N ₂ produced by the reduction of NO was measured in a temperature range of 200 to 600 ° C. by a gas chromatograph. The NO conversion rate at each temperature was determined from the amount of ₂ produced.

As a result, the platinum (P
The oxide catalyst material supporting t) was evaluated as good when it exhibits NO reduction activity in a wide range in a low temperature range of 350 ° C. or lower.

The oxide catalyst material supporting palladium (Pd) is NO in the temperature range of 350 ° C to 500 ° C.
Those showing reduction activity were evaluated as good.

[0040]

[Table 1]

As is clear from Table 1, the sample No. 1, which is a comparative example and does not carry a noble metal, shows no NO reducing activity at a temperature of 350 ° C. or lower, and the document No. 9 is out of the scope of the present invention. , 17 are N in the predetermined temperature range
O-reduction activity is low overall and not practical.

On the other hand, in the present invention, the platinum (Pt) -supported oxide catalyst exhibits a high NO reduction activity in the low temperature range of 350 ° C. or lower, and the palladium (Pd) -supported oxide catalyst does not exceed 350 ° C. It can be seen that sufficient NO reduction activity is exhibited in a wide temperature range up to 500 ° C.

Further, using the above-mentioned sample for evaluation, it was attached to the exhaust pipe of a four-cylinder diesel engine bench test apparatus, and the diesel engine was operated under the conditions of maximum rotation speed and full load.
A durability test of running for 0 hours was carried out, and the NO reduction activity of the evaluation sample after the test was evaluated in the same manner as described above.
It was confirmed that the O conversion rate did not almost decrease, and it was also proved that the water resistance and heat resistance were excellent.

[0044]

As described above in detail, according to the oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention, the oxide catalyst material contains Ni and Ga as main metal elements. Al ₂ O for spinel type complex oxide
Platinum (Pt) or palladium (Pd) is added to the carrier mixed with ₃ in an amount of 0.01 to 100 parts by weight of the carrier.
1.0 parts by weight is supported, and since the oxide catalyst material and the exhaust gas containing nitrogen oxide are contacted in an oxidizing atmosphere in which a high concentration of oxygen and a carbon-containing gas having a reducing property are present, Excellent NO _X reduction performance not only in an atmosphere in which water vapor exists but also in an atmosphere with a high oxygen concentration of 3% or more in the exhaust gas, as well as at a high gas flow rate. NO _x contained in exhaust gas
Can be effectively reduced and removed.

As a result, purification of various harmful substances containing NO _x , including exhaust gas from various internal combustion engines such as diesel engines and lean burn engines, which are developed for the purpose of energy saving, resource saving and prevention of global warming. It will be extremely useful for

Claims (6)

[Claims] 1. Platinum (Pt) or palladium is added to a carrier in which a composite oxide having a spinel structure containing nickel (Ni) and gallium (Ga) as main metal elements is mixed with alumina (Al ₂ O ₃ ). (Pd) as the carrier 10
An oxide catalyst material for removing nitrogen oxides, which is carried in an amount of 0.01 to 1.0 parts by weight based on 0 parts by weight. 2. The platinum (Pt) is 0.03 to 1.0 part by weight with respect to 100 parts by weight of the carrier, or the palladium (Pd) is 0.0 with respect to 100 parts by weight of the carrier.
The oxide catalyst material for removing nitrogen oxides according to claim 1, which is carried in an amount of 1 to 0.7 parts by weight. 3. The platinum (Pt) is 0.03 to 0.7 parts by weight with respect to 100 parts by weight of the carrier, or the palladium (Pd) is 0.0 with respect to 100 parts by weight of the carrier.
The oxide catalyst material for removing nitrogen oxides according to claim 1 or 2, wherein 1 to 0.5 part by weight is supported. 4. A composite oxide having a spinel structure and nickel containing nickel (Ni) and gallium (Ga) as main metal elements in an oxidizing atmosphere in which a high concentration of oxygen and a carbon-containing gas having a reducing property are present. An oxide catalyst material obtained by supporting platinum (Pt) or palladium (Pd) on a support mixed with (Al ₂ O ₃ ) in an amount of 0.01 to 1.0 part by weight based on 100 parts by weight of the support. A method for removing nitrogen oxide, comprising contacting with exhaust gas containing nitrogen oxide. 5. The platinum (Pt) is 0.03 to 1.0 part by weight with respect to 100 parts by weight of the carrier, or the palladium (Pd) is 0.01 with respect to 100 parts by weight of the carrier.
5. The method for removing nitrogen oxides according to claim 4, wherein the oxide catalyst material supported by about 0.7 parts by weight is brought into contact with exhaust gas containing nitrogen oxides. 6. The platinum (Pt) is 0.03 to 0.7 part by weight with respect to 100 parts by weight of the carrier, or the palladium (Pd) is 0.01 to 0.7 part by weight with respect to 100 parts by weight of the carrier.
The method for removing nitrogen oxides according to claim 4 or 5, wherein the oxide catalyst material supported by 0.5 parts by weight is brought into contact with exhaust gas containing nitrogen oxides.